Investigating static voltage stability of distribution system with rooftop PV units

Photovoltaic (PV) in high penetration level can help the static voltage stability by increasing the loadability of the system. This paper presents an analytical approach to assess the possibility of improvement in the loadability of a distribution system by real and reactive power injection from PV. In order to achieve this, a two-bus equivalent network is considered to represent the power system. The phase angles of line and load impedances of this equivalent circuit can be adjusted to reflect the characteristics of a distribution system. For different line and load parameters, change in the loadability of the system by injecting power from PV is simulated and compared. Analytical expressions, based on results from simple two-bus networks, are verified by estimating change of the loadability in IEEE-37 distribution test system.